State estimation of a faulty actuator using the second-order smooth variable structure filter (The 2ND-order SVSF)

This paper presents the application of the new developed second-order Smooth Variable Structure Filter, 2^nd-order SVSF, for fault detection under uncertain conditions. The 2^nd-order SVSF is a novel modelbased state estimation method formulated in a predictor-corrector form. It produces robust state estimation under uncertain conditions, while decreasing the measurement error and its difference, at the same time. The stability of the 2^nd-order SVSF is proven using the Lyapunov´s stability criterion with the given bounded noise and modeling uncertainties. The corrective gain of the filter is pushing the measurement error and its difference toward zero. This results in providing higher degrees of accuracy, robustness and smoothness in state estimation under uncertain situations. Due to the robust performance of the 2^nd-order SVSF for state estimation, it applies to an experimental setup of an Electro-Hydrostatic Actuator (EHA) for fault detection. Experimentation are performed for the EHA setup under the normal and faulty conditions. For the faulty EHA setup, there exists a major friction condition in the EHA´s cylinders. The robustness of the new developed 2^nd-order SVSF is then verified by comparing its performance with the state-of-the-art filters including the Kalman Filter (KF) and the 1^st-order SVSF.